U.S. Pat. application Ser. No. 843,676 filed Oct. 19, 1977, discloses a vaporization cooled transformer wherein a vaporizable fluid is used for providing both cooling facility and dielectric capability to transformer cores and windings. An effective liquid level gage for sensing the quantity of coolant is described in U.S. patent application Ser. No. 939,123 filed Sept. 5, 1978, and now abandoned. The liquid level gage adequately provides shutoff facility when a vaporizable fluid such as trichlorotrifluoroethane leaks out of the transformer tank. The aforementioned vaporization cooled transformer utilizes a quantity of molecular sieve material in the vapor path between the transformer tank and the heat exchanger as a water scavenger to remove any moisture that may be released from the cellulosic insulation materials during transformer operation. Since the insulating material continuously release water vapor to the transformer interior over the operating life of the transformer, a sufficient quantity of the molecular sieve material is employed to provide for adequate water absorption throughout the operating life of the transformer. In the event that the sieve material becomes saturated, excess moisture can occur within the transformer and behave as an ideal gas under certain temperature conditions. The excess moisture under these conditions can cause corrosion of the heat exchanger.
When leaks develop through openings occurring within the heat exchanger or tank assembly a negative internal pressure within the heat exchanger or tank assembly allows a substantial quantity of ambient air to enter through the leak openings. The presence of a quantity of atmospheric air within the heat exchanger can be detrimental to the transformer operation. One long-term deleterious effect is the premature saturation of the molecular sieve material due to the presence of substantial quantities of water vapor present within the admitted air.
Short-term deleterious effects which can occur due to the presence of the admitted air include both an overpressure condition caused by reduced heat exchanger efficiency as well as coolant loss by the escape of the vaporizable coolant out through the leak openings. The heat exchanger efficiency is decreased because the presence of the trapped air within the heat exchanger headers and cooling tubes prevents the vaporized coolant from entering into these areas during the condensation periods of the vaporization-condensation cycle. The loss in cooling efficiency in turn causes the transformer to operate at a higher temperature causing further increases in pressure until an overpressure mechanism becomes energized and the transformer becomes automatically disconnected.
The purpose of this invention is to provide means for sensing the differences in temperature that exist between the heat exchanger and the transformer tank to determine the presence of admitted air within the heat exchanger assembly as well as the presence of excess moisture.